Summary

Synthetic biologists have long sought to make cells more like computers. This is not because they think cells will be more efficient than silicon—current microelectronics make excellent computers and are less messy than cell cultures—but instead because synthetic cells can interface with biology to perform biochemical tasks. Synthetic cells might one day be capable of attacking tumors or releasing site-specific drugs inside the human body. But to carry out these tasks, synthetic biologists must be able to program cells much in the same way we program computers—by providing them with decision-making capabilities based on inputs. Indeed, prototypes of many of the genetic parts necessary for turning cells into biocomputers have been constructed, including transcriptional logic gates (1), timers (2, 3), counters (4), memory devices (5, 6), tunable sensors (7, 8), and even in vitro DNA systems that can perform complex calculations (9). On page 169 of this issue, Tang and Liu (10) expand the capabilities of cellular computers by engineering a new memory device that records events directly onto DNA.